Avoid the device select overhead on every qc_issue (> 10uS) by caching the
currently selected device. This shows up on profiles under load.
Signed-off-by: Alan Cox <alan@xxxxxxxxxxxxxxx>
---
drivers/ata/libata-sff.c | 6 +++++-
include/linux/libata.h | 1 +
2 files changed, 6 insertions(+), 1 deletions(-)
diff --git a/drivers/ata/libata-sff.c b/drivers/ata/libata-sff.c
index 4b57ae9..4fb1229 100644
--- a/drivers/ata/libata-sff.c
+++ b/drivers/ata/libata-sff.c
@@ -470,6 +470,7 @@ void ata_sff_dev_select(struct ata_port *ap, unsigned int device)
iowrite8(tmp, ap->ioaddr.device_addr);
ata_sff_pause(ap); /* needed; also flushes, for mmio */
+ ap->sff_selected = device;
}
EXPORT_SYMBOL_GPL(ata_sff_dev_select);
@@ -1559,7 +1560,8 @@ unsigned int ata_sff_qc_issue(struct ata_queued_cmd *qc)
}
/* select the device */
- ata_dev_select(ap, qc->dev->devno, 1, 0);
+ if (qc->dev->devno != ap->sff_selected)
+ ata_dev_select(ap, qc->dev->devno, 1, 0);
/* start the command */
switch (qc->tf.protocol) {
@@ -1971,6 +1973,8 @@ int ata_sff_prereset(struct ata_link *link, unsigned long deadline)
struct ata_eh_context *ehc = &link->eh_context;
int rc;
+ link->ap->sff_selected = -1; /* Unknown */
+
rc = ata_std_prereset(link, deadline);
if (rc)
return rc;
diff --git a/include/linux/libata.h b/include/linux/libata.h
index c4811d9..63a9489 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -727,6 +727,7 @@ struct ata_port {
#ifdef CONFIG_ATA_SFF
struct ata_ioports ioaddr; /* ATA cmd/ctl/dma register blocks */
+ int sff_selected; /* Cache of selected device */
#endif /* CONFIG_ATA_SFF */
u8 ctl; /* cache of ATA control register */
--
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